1. Field
The disclosed embodiments generally relate to techniques for calibrating antenna arrays. More specifically, the disclosed embodiments relate to a method and apparatus for calibrating a retro-directive antenna array to support an asymmetric wireless link.
2. Related Art
In wireless communication systems, performance can be improved by using multiple antennas to directionally transmit and receive electromagnetic signals. For example, a phased-array antenna system comprising multiple antenna elements and associated signal-processing circuitry can be used to directionally transmit and receive an electromagnetic beam. In such systems, the direction of the beam can be steered by adjusting the phase relationships between the signals associated with the constituent antenna elements. In another example, tracking systems based on phase arrays have been used for many years in military radar applications.
Recent technological developments are beginning to make it practical to apply these technologies to asymmetric wireless consumer applications, for example to track a controller device from a game console. In contrast to military radar applications, the targets for consumer applications can cooperate to ease the tracking process. However, the only practical frequency band for such applications is in the millimeter-wavelength range, which facilitates fitting a small antenna array with a reasonable number of elements to provide fine beam resolution inside a portable device, such as a game controller.
Unfortunately, manufacturing process variations in such systems can cause signals to have both phase and magnitude errors. Moreover, at higher frequencies, these errors are more pronounced because the absolute values of circuit parameters such as inductance (L) and capacitance (C) scale with frequency while the associated variations do not. Furthermore, in systems that use antenna arrays, these errors are more significant because the mismatch between circuit elements can additionally reduce system performance.